In the art of the present invention, there has been a consensus that an epithelial sodium channel (also referred to as “ENaC”) is a salty-taste receptor (Non-patent document 1). In addition, it has been known that mice have a salty-taste reception system via ENaC and another unknown salty-taste reception system (Non-patent document 2). It has been considered that ENaC is responsible for approximately half of salty-taste reception (taste nerve responses to salty taste) in mice (Non-patent document 1).
It has been reported that the Kv3.2 protein generates sodium current, i.e. functions as a sodium channel (Patent document 1). In addition, an activator substance of the Kv3.2 protein slightly showed a salty-taste enhancing effect in sensory evaluation (Patent document 1).
The TMC6 protein, which is encoded by the TMC6 gene, has been predicted to be a ten-pass transmembrane protein and an ion channel on the basis of the amino acid sequence thereof. In addition, it has been known that disruption of the TMC6 gene results in a decrease in immune functions (Non-patent documents 3-4). However, the actual function of the TMC6 protein has not been identified.